1. Field of the Invention
This invention relates to pressure-sensitive adhesives.
2. Introduction to the Invention
Pressure-sensitive adhesives, which are often referred to as PSA's, are well known. They are viscoelastic materials which, in solvent-free form, remain permanently tacky and will adhere instantaneously to a wide variety of solid surfaces as a result of the application of very slight pressure. A PSA is usually used in the form of a solvent-free coating on a backing, often a flexible backing, for example a paper label or a polymeric tape. Such PSA-coated backings are referred to herein as PSA composites.
In some uses of PSA composites, it is desirable to remove the PSA composite from the receptor (i.e. the surface to which the PSA has been applied) and to do so cleanly, i.e. without leaving any adhesive residue on the receptor. In situations which call for such removal, known PSA composites often leave adhesive residue on the receptor, and/or require more force than is desirable for their removal, for example causing the backing or the receptor to tear (or otherwise deform). These problems are particularly severe in the medical field, when PSA composites must be removed from the human skin; and in situations in which the PSA composite has been attached to the receptor for a long time, since this can increase the strength of the adhesive bond between the receptor and the PSA, and/or decrease the cohesive strength of the PSA, and/or reduce the tackiness of the PSA.